"Everyone is the hero of their own story." is a popular claim, and may well be true, but I don't know if any evidence for it has been carefully collected.
"The Enemy's story, as seen by the Enemy, is not going to make the Enemy look bad."
Some cultures fairly reliably create people who think rap sounds bad, others fairly reliably create people who think rap sounds good.
Some cultures fairly reliably create people who think sushi tastes bad, others fairly reliably create people who think sushi tastes good.
Some cultures fairly reliably create people who think saying that the best thing in life is "To crush your enemies, see them driven before you, and to hear the lamentation of their women" is bad, others fairly reliably create people who think this, or suttee, or gladiatorial combat, or mortification of the flesh of various types, or honor murder, or military heirarchy, or pederasty or... make people look good.
"If it took a mutant to do monstrous things, the history of the human species would look very different." but if "violence [was] a typically human response" to the global situation as seen by some cultural groups prior to 9/11 then recent history would also look very different. In fact, the number of terrorists in the world is quite small, which I take to be a really really good reason for not killing random Muslims who kind-of-sort-of look the same. Terrorists are much much rarer than Scientologists or Jesus Camp victims, and for this reason one might think them much more likely to "send shivers of serious horror down your spine".
You know that most cops never kill anyone, right?
"in another world, if they had been raised in a different environment" seems like a weird exculpatory justification. One with weirdly much in common with calling a foetus a potential human being, as if almost every human cell did also not contain a recipe for a potential human being and as if every large lump of organic matter didn't have the potential to be one if processed correctly. I mean really, surely we could, if we wanted to, find tissue samples from every victim of violence who we identified and clone them, but would we then rightly feel that the tragedy of them being raised in the wrong environment had been corrected?